1. Field of the Invention
This invention relates to display systems and, more particularly, to a system for scrolling windows of text characters and graphic data in a color graphics raster scan, all points addressable, video display.
2. Discussion of the Prior Art
A video display typically provides an interface between a data processing system and a user. Such video displays may be used to display text characters, such as instructions and data, and graphic information such as charts, graphs, diagrams, and schematics, to the user. In many applications, it is desirable to scroll the character and/or graphic information, or some portion or window thereof, to move some of the information off of the screen to be replaced by new information entered by the user at a keyboard, or else supplied to the screen by the data processing system. U.S. Pat. No. 4,196,430 "Roll-up Method for a Display Unit" describes such a system. In this reference, a refresh memory including a data portion for specifying character text data and a control portion for specifying such control parameters as blinking and shading attributes is stored in a random access memory. Text data from the data portion is fed to a character generator, which supplies text character dot image information to a CRT display. Scrolling of selected windows, or portions of the display, is accomplished by means of a roll-up instruction which is executed to transfer partial rows of data and/or control information within the refresh memory. However, in U.S. Pat. No. 4,196,430, there is no provision for the scrolling of windows containing graphic information, nor for the scrolling of windows containing both graphic information and text characters.